SurfaceMask should be copied properly.

#1331

worldedit-core/src/main/java/com/fastasyncworldedit/core/function/mask/AdjacentAnyMask.java

@@ -12,8 +12,8 @@ public class AdjacentAnyMask extends AbstractMask implements ResettableMask {
 
     private final CachedMask mask;
     private final MutableBlockVector3 mutable;
-    private final int minY;
-    private final int maxY;
+    final int minY;
+    final int maxY;
 
     public AdjacentAnyMask(Mask mask, int minY, int maxY) {
         this.mask = CachedMask.cache(mask);
@@ -22,6 +22,13 @@ public class AdjacentAnyMask extends AbstractMask implements ResettableMask {
         this.maxY = maxY;
     }
 
+    AdjacentAnyMask(CachedMask mask, int minY, int maxY) {
+        this.mask = CachedMask.cache(mask);
+        mutable = new MutableBlockVector3();
+        this.minY = minY;
+        this.maxY = maxY;
+    }
+
     @Override
     public void reset() {
         mutable.setComponents(0, 0, 0);
@@ -59,7 +66,7 @@ public class AdjacentAnyMask extends AbstractMask implements ResettableMask {
 
     @Override
     public Mask copy() {
-        return new AdjacentAnyMask(mask.copy(), minY, maxY);
+        return new AdjacentAnyMask((CachedMask) mask.copy(), minY, maxY);
     }
 
 }

worldedit-core/src/main/java/com/fastasyncworldedit/core/function/mask/SurfaceMask.java

@@ -12,6 +12,10 @@ public class SurfaceMask extends AdjacentAnyMask {
         super(getMask(extent), extent.getMinY(), extent.getMaxY());
     }
 
+    private SurfaceMask(CachedMask mask, int minY, int maxY) {
+        super(mask, minY, maxY);
+    }
+
     public static AbstractExtentMask getMask(Extent extent) {
         return new BlockMaskBuilder()
                 .addTypes(BlockTypes.AIR, BlockTypes.CAVE_AIR, BlockTypes.VOID_AIR)
@@ -26,8 +30,8 @@ public class SurfaceMask extends AdjacentAnyMask {
 
     @Override
     public Mask copy() {
-        // The mask is not mutable. There is no need to clone it.
-        return this;
+        // CachedMask (super getParentMask) should not be used from multiple threads.
+        return new SurfaceMask(getParentMask(), minY, maxY);
     }
 
 }